The use of metal cyclopentadienyl complexes for the polymerization of olefins and diolefins, particularly the use of metallocene complexes in admixture with activating co-catalysts, has long been known.
U.S. Pat. No. 2,827,446 describes a catalyst which is prepared from titanocene dichloride and diethylaluminum chloride for the polymerization of ethylene. However, this catalyst is unsuitable for industrial use, since first, the activity of the catalyst is too low and second, the polymerization of 1-olefins is not possible.
Highly effective, specific catalyst systems are known for the (co)polymerization of ethylene and/or 1-olefins. These catalysts consist of metallocene dichlorides in admixture with aluminoxanes, e.g. methylaluminoxane (MAO). In order to increase the activity and selectivity of the catalyst and in order to control the microstructure, molecular weight and molecular weight distribution of the products, a multiplicity of new metallocene catalysts or metallocene catalyst systems has been developed in recent years for the polymerization of olefinic compounds (e.g. EP 69,951, 129,368, 347,128, 347,129, 351,392, 485,821, 485,823). Chlorine-containing metallocenes are usually employed in combination with MAO.
Methods of polymerizing olefins are also known in which metallocene/aluminoxane catalysts (e.g. EP 308,177) are produced in situ.
In WO 97/07141, fluorine-containing semi-sandwich complexes of titanium are used in combination with MAO as catalysts for the production of polystyrene. WO 98/36004 describes fluorine-containing complexes, preferably of titanium, and preferably in combination with MAO, as catalysts for the production of polybutadiene.
However, the catalyst systems based on aluminoxanes, e.g. MAO, which were described above have disadvantages which are described in greater detail below. MAO is a mixture of different aluminum compounds, the number and structure of which are not known accurately. The polymerization of olefins with catalyst systems which contain MAO is therefore, not always reproducible. Moreover, MAO is not stable on storage and its composition changes under the effect of thermal stresses. MAO has the disadvantage of having to be used in considerable excess in order to achieve high catalyst activities and this results in a high content of aluminum in the polymer. MAO is also a cost-determining factor. Considerable excesses of MAO are uneconomic for industrial use.
In order to circumvent these disadvantages, aluminoxane-free polymerization catalysts have been developed in recent years. For example, Jordan, et al. in J. Am. Chem. Soc., Vol. 108 (1986), 7410 describe a cationic zirconocene-methyl complex which contains tetraphenylborate as a counterion and which polymerizes ethylene in methylene chloride. EP-A 277,003 and EP-A 277,004 describe ionic metallocenes which are prepared by the reaction of metallocenes with ionizing reagents. EP-A 468,537 describes catalysts which possess an ionic structure and which are prepared by the reaction of metallocene dialkyl compounds with tetrakis(pentafluorophenyl)boron compounds. Ionic metallocenes are suitable as catalysts for the polymerization of olefins. One disadvantage, however, is the high sensitivity of these catalysts to impurities, such as moisture and oxygen, for example.
Prior art methods of preparing cationic metallocene complexes also have the disadvantage that the reagents which result in cation formation, e.g. tetrakis(pentafluorophenyl)boron compounds, are sometimes costly to synthesize, and the use thereof is expensive.
In addition, methods are known for the polymerization of olefins in which metallocene dialkyl compounds (EP 427,697) or metallocene dichlorides (WO 92/01723), each in combination with aluminum alkyls and a third component, e.g. tris(pentafluorophenyl)boron compounds, are used as catalyst systems. Metallocene dichlorides or metallocene dialkyls in combination with aluminum alkyls alone, are not active with regard to polymerization.